Plastic substrates are widely used in the fabrication of electronic devices, particularly in the microelectronic industry, due to advantages over glass substrates. Some of these advantages include flexibility, lighter weight, thinness, and robustness. Other advantages to the use of plastic substrates include good processability and impact resistance, making it an attractive substrate for an endless variety of applications.
However, one disadvantage to the use of plastics in an application can be relatively low surface hardness and ease of being scratched. This may particularly pose a problem in applications that require good transparency. Electronic devices with plastic substrates have another disadvantage relating to oxygen and moisture diffusion—plastic substrates are generally not impervious to oxygen and water vapor, and thus may not be suitable for the manufacture of certain devices such as organic light-emitting diodes (OLEDs), which may otherwise benefit from properties of the plastic.
In order to improve the resistance of these substrates to oxygen and water vapor, coatings comprising ceramic materials have been applied to a surface of the plastic substrate. Plasma assisted coating and etching processes have been widely used in the microelectronic industry, particularly in the semiconductor manufacturing industry to deposit films onto wafers or other temperature-sensitive structures. One reason for use of plasma assisted coating and etching processes is that plasmas are capable of efficiently generating chemically active species. Second, plasma can generate ions and accelerate the ions to energies of 50-1000 eV in the vicinity of the deposition or etching substrate. Plasma assisted deposition can add impermeability and/or gas-barrier properties to a substrate, and can be useful for the protection of plastics against scratching and abrasion. Such processes including plasma enhanced chemical vapor deposition (PECVD), plasma assisted evaporation, plasma assisted atomic layer deposition (ALD), reactive ion etching (RIE), and the like. Often these coatings deposited by such processes are of a “silica” type.
However, there can be certain technical challenges associated with plasma assisted coating and etching processes on plastic substrates. For example, plastic substrates typically have a relatively high coefficient of thermal expansion (CTE) compared to a metal electrode employed in the plasma reactor. A material's CTE indicates its expansion and contraction properties as a function of temperature. Furthermore, plastic substrates shrink after heating at elevated temperatures. Unlike thermal expansion, shrinkage is generally irreversible. Thermal expansion combined with shrinkage can therefore cause the article to curl significantly during the heating and cooling processes, which may pose significant challenges during manufacturing. The CTE mismatch between the plastic and the metal results in non-uniform gap between plastic substrate and metal electrode and causes non-uniform deposition, coating density, and deposition rate across the substrate surface.
Certain methods have been employed to address this problem. For example, mechanical methods exist in order to keep the polymeric substrate in good contact with the metallic electrode. However, such mechanical methods can require modifying deposition hardware, incurring extra time, labor, and processing costs.
Therefore, there exists a need for new approaches for achieving uniform film deposition or etching during processing.